Including the simultaneous terrorist bomb explosion incidents that occurred in Great Britain in 2005, terrorist bomb explosion incidents have occurred frequently at public facilities and public transportation in recent years. In recent times, there have been growing cases where a dangerous character, such as a terrorist, pretending to be a passenger carries onto an airplane or the like an optically transparent container for a drink, such as a PET bottle, or a glass bottle, for example, filled with a liquid in which an explosive, a raw material for explosive, or the like has been mixed or dissolved. Further, there have also been growing cases where a liquid, in which an illicit drug such as a narcotic or a stimulant has been dissolved, is smuggled in a manner that an optically transparent container is filled with the illicit drug.
As measures against the carrying of explosives, a raw material for explosive, and illicit drugs on airplanes, hand luggage inspections are conducted on passengers at airports for preventing occurrence of incidents such as terrorist incidents, and smuggling. In order to conduct inspections on many passengers, there is a need to swiftly conduct the inspections, but it is not easy to determine whether or not a liquid with which a container has been filled contains an explosive, a raw material for explosive, or an illicit drug during short-time inspection.
As a method for inspecting a liquid from outside a container without opening the container under such circumstances, a detection method has already been proposed which is used to swiftly determine whether a liquid is a combustible liquid, such as gasoline, or not (see Non-Patent Document 1). In such a detection method, the determination whether a liquid is a dangerous substance or not is made based on a fact that water, the main ingredient in a regular drink is different in permittivity from combustibles such as gasoline, specifically based on a fact that water is higher in permittivity than gasoline.
However, there have been growing cases where a dangerous substance close to water in permittivity is used in recent times; for example, in the foregoing incident that occurred in Great Britain, a mixed solution of hydrogen peroxide and acetone was used as an explosive. Therefore, as to detection of dangerous liquid substance close to water in permittivity, the detection method described in Non-Patent Document 1 is not an effective detection method.
On the other hand, in the USA, a device is commercially available which is capable of detecting a hydrogen peroxide solution from outside an optically transparent container by means of Raman spectroscopy. However, in the case where Raman spectroscopy is used, since optically transparent containers and liquids in the containers show strong fluorescence, necessary detection sensitivity can be hardly obtained; therefore the fact is that the device is scarcely in practical use.